The present invention relates generally to cervical fixation devices and more particularly to an improved screw pin structure that is used in connection with a cervical fixation device. Cervical fixation devices are typically used to immobilize the head and neck of a patient having suffered cervical trauma.
In the field of cervical fixation devices several different types of skull pins have been proposed and used. For example, in U.S. Pat. Nos. 4,612,930, 5,042,462, 5,122,132, and D313,471 to Bremer, and 5,347,894 to Fischer such cervical fixation devices are disclosed. As shown in these patent references, skull pins are used to secure a halo cervical fixation or similar device in a predetermined and aligned manner to a patient's skull.
Some problems and difficulties have been found, however, when a person wearing a cervical fixation device is scanned using a Magnetic Resonance Imaging (MRI) procedure. Magnetic Resonance Imaging is a technique in which an object placed in a spatially varying magnetic field is subjected to a pulse of radio frequency radiation, and the resulting nuclear magnetic resonance spectra are combined to give cross-sectional images. MRI procedure devices may be used on patients wearing cervical fixation devices to monitor the healing development of the trauma in the patient's body.
The skull pins used in the prior art cervical fixation devices have been found to act like an antenna, receiving the ambient radio frequency energy generated by the MRI. The prior art skull pin structures have been found to act as a vehicle for the conduction of radio frequency energy generated by the MRI to the patient's skin, which in effect, acts as a ground for the antenna. This phenomenon creates a sensation of heating of the skull pin at the point of contact with the patient's skin. In addition, the vibrations caused by the magnetic field generated by the MRI are transmitted through the skull pins to the patient's skin also creating a heating sensation. Prior art skull pins are typically constructed of a conductive metallic composition conducive to electrical and thermal transfer.
In summary, the phenomenon of heating of the skull pin by the above sources causes discomfort to the patient and raise issues of patient safety and comfort when wearing a cervical fixation device in an MRI procedure. Furthermore, the skull pins developed to solve this problem have been constructed with either a ceramic tip or an entire ceramic body. The ceramic material has been found to be prone to breakage because of its inherently brittle composition.
The hybrid skull pins of the present invention are provided to alleviate these problems. The term hybrid skull pin, for the purpose of this application, means a skull pin having two or more different compositions or types of structures in its embodiment.
The hybrid skull pin of the present invention is constructed of a hybrid material composition and is provided with at least a nonconductive tip that reduces or eliminates the "grounding effect" and which has the structural integrity to secure a cervical fixation device when engaged with the skull of the patient.